A German serial killer nurse was jailed for life on Thursday for the murder of 85 patients in his care, according to a statement from a court in the northwest city of Oldenburg.

Niels Hoegel, a 42-year-old former nurse who is considered Germany's deadliest post-war serial killer, was sentenced to life in prison at the District Court of Oldenburg.

While summing up the trial, the judge said Hoegel's actions were "incomprehensible: That's the word that characterizes this."

The health worker had previously confessed to killing 100 patients -- aged between 34 and 96 years old -- at two hospitals in northern Germany between 2000 and 2005. However Hoegel was acquitted of 15 cases on Thursday because there was not enough evidence.

Hoegel was accused of giving his victims various non-prescribed drugs, in an attempt to show off his resuscitation skills to colleagues and fight off boredom.

In past hearings, Hoegel said he felt euphoric when he managed to bring a patient back to life, and devastated when he failed.

Police suspect the true death toll may be as high as 200, but can't be certain as many patients were cremated before autopsies could be performed, reported Agence France-Presse news (AFP) agency.

The former nurse is already serving a life sentence for six convictions, including homicide and attempted homicide in 2008 and 2015. Those convictions led authorities to investigate hundreds of deaths and exhume the bodies of former patients in the clinics where he worked.

Hoegel asked his victims' families for forgiveness on Wednesday for his "horrible acts."

"I would like to sincerely apologize for everything I did to you over the course of years," he said during the hearing, AFP reported.

'Collective amnesia'

One of the biggest questions in the case is how Hoegel was able to murder so many people apparently under the watch of hospital staff.

Former colleagues at the Delmenhorst clinic where he worked admitted to having had their suspicions about Hoegel, according to AFP. But all the staff from the other hospital in Oldenburg who testified said they were oblivious to the rising death toll.

During sentencing Judge Sebastian Buehrmann criticized what he called staff's "collective amnesia," adding that Hoegel's killing spree was "incomprehensible."

About 126 relatives of the victims are co-plaintiffs in the trial, which has been running since October 2018.

The most successful tyranny is not the one that uses force to assure uniformity but the one that removes the awareness of other possibilities, that makes it seem inconceivable that other ways are viable, that removes the sense that there is an outside.